Gas inlet system for wet gas scrubber

ABSTRACT

A gas inlet system for a wet gas scrubber includes a weir configured to deliver liquid to a scrubbing passage to wet the interior surface of the scrubbing vessel during operation of the gas inlet system. The weir include a weir duct and a weir trough extending at least partially around the weir duct to receive and at least partially fill with liquid during operation of the gas inlet system. The weir trough has an upper trough outlet in liquid communication with the upper weir duct inlet to deliver liquid from the weir trough into the upper weir duct inlet during operation of the gas inlet system. The weir trough also has a lower trough outlet below the upper trough outlet. The lower trough outlet is in liquid communication with the scrubbing passage to deliver liquid from the weir trough toward the scrubbing passage during operation of the gas inlet system.

FIELD OF THE DISCLOSURE

The present invention generally relates to a gas inlet system for a wetgas scrubber and an associated method of scrubbing a gas for separationand removal of particulate and gaseous components from gaseousindustrial process streams.

BACKGROUND OF THE DISCLOSURE

Various industrial processes produce gaseous streams containingparticulate and gaseous components (e.g., sulfur oxides and other sulfurcompounds such as SO₂, SO₃, H₂S and H₂SO₄). Such processes include, butare not limited to, for example, fossil fuel-fired power plants, naturalgas treatment plants, refineries (e.g., fluid catalytic cracking (FCC)units), sulfur recovery units (SRUs), sulfuric acid plants, metalroasting operations, cement kilns and synthesis gas plants. Before suchgas streams can be vented to the atmosphere, they must often be treatedto remove the particulate and gaseous impurities.

Gas-liquid contacting devices in which the gaseous stream to be treatedcontacts an aqueous scrubbing liquid are employed to treat and removeparticulate and gaseous impurities from gaseous industrial processstreams. For example, in acid production processes, wet gas scrubbersmay be used to remove acid gases and particulates from flue gas. Thereare many types of wet gas scrubbers in the marketplace. However, nearlyall wet gas scrubbers share some common characteristics. In most cases,flue gas from the process is not saturated. However, before acid gasessuch as SO₂ can be removed, the gas stream must be adiabaticallysaturated or “quenched”. Most scrubbers will have a section where liquid(e.g., the scrubbing liquid) is contacted with the incoming flue gas toadiabatically saturate, or “quench,” the gas stream. Only after the gashas been quenched can acid gas and SO₂ removal occur. This isaccomplished in two steps: 1) the acid gases are absorbed into thescrubbing liquid; and 2) once absorbed, the acid gases react with areagent, forming reaction by-products that are then removed from theclean gas. In general, all scrubbers have a method for removing thewater droplets and reaction by-products from the gas before the treatedgas is discharged from the scrubber.

Gas-liquid contacting devices capable of handling hot and/or corrosivegaseous effluents and operating at high overall liquid to gas ratio(L/G) are often preferred. For example, gas scrubbing systems comprisinga reverse jet scrubber of the type disclosed in U.S. Pat. No. 3,803,805and sold under the trademark DYNAWAVE by MECS, Inc. (Chesterfield, Mo.U.S.A. 63017) are particularly suited for effective separation andremoval of particulate and gaseous components from hot gas streams.

Reverse jet scrubbers typically include a gas inlet system and agas-liquid disengagement vessel downstream of the gas inlet system. Thegas inlet system includes a scrubbing vessel that receives the hot,corrosive gas and brings the gas in contact with an intense spray ofscrubbing liquid emitted from one or more reverse jets to quench the gasstream and absorb acid gas impurities into the scrubbing liquid andremove particulate contaminants. To prevent thermal and corrosive damagein the vicinity of the hot gas inlet, the upper region of the reversejet scrubbing vessel is kept cool and cleaned by a continuously flowingliquid film produced by feeding a portion of the scrubbing liquid intothe reverse jet scrubber my means of an overflow or leaping weir asdescribed, for example in Canadian Published Application No. 2,050,710.In particular, the overflow weir forms a continuous, flowing film ofliquid (such as circulating scrubbing liquid) along the interior surfaceof the scrubbing vessel in the vicinity of the hot gas inlet. Theoverflow weir typically includes a weir trough or bowl that fills withliquid and overflows into the scrubbing vessel. This film of flowingliquid protects the equipment from high temperature, and/or excessivecorrosion.

However, the effectiveness of reverse jet scrubbing systems cansometimes be adversely affected by the build-up of suspended particlesin the circulating scrubbing liquid. The circulating liquid introducedinto the scrubbing vessel through the weir often contains suspendedparticles, such as metal oxides and/or fly ash, that can settle out anddeposit in the weir. During operation of the gas inlet system, some ofthe particulates disengage from the liquid in the weir trough and settleat the bottom of the weir trough. Over time, the particulates mayaccumulate in the weir trough, leading to problems such as non-uniformoverflow of liquid in the weir. In turn, the non-uniform overflow ofliquid may lead to dry areas on the interior surface of the scrubbingvessel, which can result in corrosion and ultimately failure of the gasinlet system.

Particulate impurities can be purged from the scrubbing liquidcirculating in a reverse jet wet scrubber system. For example, externaldrains in fluid communication with the weir trough and actuated on anintermittent basis can be used to eliminate the solids that settle outin the weir bowl. In one example, the external drain includes a funnelat the bottom of the weir trough in which disengaged particulates settleand accumulate. An external valve is fluidly connected to the funnel.The valve is periodically opened to allow for flushing and removal ofparticulates in the funnel.

Although the overflow weir and the external drains have worked quitewell in most applications, the inventors of the claimed invention haveidentified several potential issues with the overflow weir and theexternal drains, as described below. The inventors do not concede thatthese issues are known in the prior art or readily identifiable to thoseof ordinary skill in the art.

The external drains may be costly to fabricate and install at the site,and require external piping, valves, wiring and heat tracing. Moreover,because these external drains operate on an intermittent basis, if thepurge cycle is disrupted for any reason, including valve failure,operator error, equipment failure, etc., the liquid film can bedisrupted and the equipment damaged by the corrosive gas. If overflowwas disrupted along the upper end of the weir, for whatever reason, adry spot(s) may occur in the scrubbing vessel. The dry spot may lead tocorrosion and/or overheating of that area of the vessel, and ultimatelyfailure of the gas inlet system. Moreover, if solids build up tooquickly, the external drains could become clogged. When this happens,additional solids would settle until flow over the upper end of the weiris disrupted. As another example, the external drain valves could eitherfail to open, which would cause solids build-up, or they could remainopen too long, and disrupt flow over the weir.

Accordingly, in view of the above-identified potential issues withconventional gas inlet systems, a need persists for improved weir andgas inlet system designs for wet gas scrubbers that provide foreffective, continuous removal of accumulating solid impurities from thecirculating scrubbing liquid.

SUMMARY OF THE DISCLOSURE

In one aspect, a gas inlet system for a wet gas scrubber generallycomprises a scrubbing vessel and a weir. The scrubbing vessel has aninterior surface defining a scrubbing passage and is configured toreceive a gas and a scrubbing liquid so that the gas contacts thescrubbing liquid during operation of the gas inlet system. The weir isdisposed above and in fluid communication with the scrubbing passage.The weir is configured to deliver liquid to the scrubbing passage to wetthe interior surface of the scrubbing vessel during operation of the gasinlet system. The weir includes a weir duct and a weir trough. The weirduct has at least one side wall, an interior weir duct passage, an upperweir duct inlet in fluid communication with the interior weir ductpassage, and a lower weir duct outlet in fluid communication with theweir duct passage. The weir trough extends at least partially around theat least one side wall of the weir duct and is configured to receive andat least partially fill with liquid during operation of the gas inletsystem. The weir trough has an upper trough outlet in liquidcommunication with the upper weir duct inlet and is configured todeliver liquid from the weir trough into the upper weir duct inletduring operation of the gas inlet system, whereby liquid is directedfrom the weir duct passage through the lower weir duct outlet and towardthe scrubbing passage to facilitate wetting of the interior surface ofscrubbing vessel during operation of the gas inlet system. The weirtrough has a lower trough outlet below the upper trough outlet. Thelower trough outlet is in liquid communication with the scrubbingpassage and configured to deliver liquid from the weir trough toward thescrubbing passage during operation of the gas inlet system.

In another aspect, a method of scrubbing a gas generally comprisesfilling, at least partially, a weir trough of a gas inlet system of agas scrubber with a liquid. The weir trough is disposed above ascrubbing passage defined by a scrubbing vessel and at least partiallysurrounds a weir duct defining a weir duct passage. Liquid is deliveredfrom the weir trough through an upper trough outlet of the weir troughand into the weir duct passage. Liquid exiting the upper trough outletflows through the weir duct passage and subsequently flows downward intothe scrubbing passage and facilitates wetting of an interior surface ofthe scrubbing vessel defining the scrubbing passage. Liquid is deliveredfrom the weir trough through a lower trough outlet of the weir troughand into the scrubbing passage. Liquid exiting the lower trough outletfacilitates wetting of the interior surface of the scrubbing vesseldefining the scrubbing passage. A gas and a scrubbing liquid areintroduced into the scrubbing passage such that the gas and scrubbingliquid contact one another.

Other features will be in part apparent and in part pointed outhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of one embodiment of a gas scrubber including agas inlet system and a gas-liquid disengagement vessel;

FIG. 2 is a front elevation of the gas inlet system, including a weirand a scrubbing vessel;

FIG. 3 is a top plan view of the gas inlet system of FIG. 2;

FIG. 4 is a cross section taken through the plane defined by the line4-4 in FIG. 2;

FIG. 5 is an enlarged, partial longitudinal section of an upper portionof the gas inlet system of FIG. 2;

FIG. 6 is an enlarged, partial view of an upper portion of the crosssection of FIG. 5; and

FIG. 7 is an enlarged, partial view of a lower portion of the crosssection of FIG. 5.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring to FIG. 1, a schematic of one embodiment of a wet gas scrubberis generally indicated at reference numeral 10. The illustrated wet gasscrubber 10 includes a gas inlet system, generally indicated at 12, anda gas-liquid disengagement vessel, generally indicated at 14, in fluidcommunication with the gas inlet system. In general, and as explained inmore detail below, the gas inlet system 12 is configured to receive gas(e.g., hot gas) effluent from an industrial process and bring the hotgas in contact with a scrubbing liquid to both cool the hot gas andremove contaminants from the gas. As an example, the hot gas effluentmay be derived from metal roasting operations. After coming into contactwith one another within the gas inlet system 12, the wet gas and thespent scrubbing liquid exit the gas inlet system through an outlet 16and enter the gas-liquid disengagement vessel 14. Within the gas-liquiddisengagement vessel 14, the spent scrubbing liquid and the wet gasdisengage or separate so that the spent scrubbing liquid collects in alower sump 18 and the wet gas flows upward through a gas outlet duct ortower 20. The spent scrubbing liquid in the sump 18 is recycled anddelivered back to the gas inlet system 12 via a pump 22. The wet gas inthe tower 20 flows through a demister 24 (e.g., chevron) and/or othergas/liquid separation devices before exiting the tower through a toweroutlet 26. The foregoing brief descriptions of some of the components ofthe illustrated wet gas scrubber 10 are generally known in the art, andother processes or devices may be included in the wet gas scrubberwithout departing from the scope of the present invention defined by theclaims.

As shown generally in FIG. 1, the illustrated gas inlet system 12includes a scrubbing vessel, generally indicated at 30, a jet nozzle 32within the scrubbing vessel for delivering the scrubbing liquid into thescrubbing vessel, and a weir, generally indicated at 34, in fluidcommunication with and disposed above the scrubbing vessel. As describedin more detail below, the weir 34 is configured for wetting an interiorsurface 36 (see, e.g., FIG. 2) of the scrubbing vessel 30 defining ascrubbing passage 37. A gas inlet tube 38 extends through an open upperend of the weir 34 for delivering hot gas into the scrubbing vessel 30.The hot gas from the gas inlet tube 38 flows in a downward direction inthe scrubbing passage 37, and the scrubbing liquid from the jet nozzle32 flows in an upward direction in the scrubbing passage. The hot gasand the scrubbing liquid collide with one another to create a turbulentzone 40 (called a “froth zone”) within the scrubbing passage 37. In thefroth zone 40, the gas/liquid interface is continuously and rapidlyrenewed. When the momentum of the gas and liquid balances, the liquidreverses direction and flows downward in the scrubbing passage 37. Thescrubbed gas and the spent liquid exit the scrubbing vessel 30 and enterthe gas-liquid disengagement vessel 14, as explained above. As isgenerally known in the art, the illustrated wet gas scrubber 10 isgenerally of the type referred to as a “counter-current scrubber”because hot gas and scrubbing liquid flow in opposing directions withinthe scrubbing vessel 30. It is understood that in other embodiments, thewet gas scrubber 10 may be a “co-current scrubber,” whereby the hot gasand the scrubbing liquid flow in the same direction (e.g., a downwarddirection) within the scrubbing vessel 30. The gas inlet system 12 mayinclude other types of scrubbing vessels without departing from thescope of the present invention.

Referring to FIGS. 2 and 3, the weir 34 of the gas inlet system 12 isconfigured to wet the interior surface 36 of the scrubbing vessel 30 byforming a film or layer of liquid flowing downward over the interiorsurface during operation of the gas inlet system. The liquid may bescrubbing liquid and may come from the same source as the scrubbingliquid delivered through the jet nozzle 32, as explained below. The weir34 includes an outer weir receptacle, generally indicated at 44, and aninner weir duct, generally indicated at 46, received in the weirreceptacle.

Referring to FIG. 5, the weir receptacle 44 has a side wall 48, openupper and lower ends 50 a, 50 b, respectively, and an interior surface52 defining an interior space in which the weir duct 46 is received. Thelower end 50 b of the weir receptacle 44 defines an outlet 56 of theweir that is in fluid communication with the scrubbing vessel 30. Theinterior surface 52 at an upper portion 58 of the weir receptacle 44 hasa generally annular shape, and the interior surface at a lower portion60 of the weir receptacle has a generally cone shape that tapers orslopes downward toward the open lower end 50 b of the weir receptacle.The weir duct 46 has a side wall 62, an interior surface 64 defining aninterior duct passage 66, an upper duct inlet 68 in communication withthe interior duct passage, and a lower duct outlet 70 in communicationwith the duct passage. In the illustrated embodiment, the upper ductinlet 68 is defined by an upper end of the weir duct 46, and the lowerduct outlet 70 is defined by a lower end of the weir duct. The weir duct46 has a generally cylindrical shape with a weir lip 72 extendinglaterally outward at the upper end of the duct. A securement flange 78extends laterally between and interconnects the weir duct 46 and theweir receptacle 44 to fixedly secure the duct in the receptacle. Thesecurement flange 78 has an annular shape and extends around a perimeterof the side wall 62 of the weir duct 46, although the securement flangemay be of other shapes. For reasons explained below, the securementflange 78 has at least one opening 80, and in the illustratedembodiment, the securement flange has a plurality of openings (as shownin FIG. 3) spaced apart from one another around the securement flange.Also for reasons explained below, as secured within the weir receptacle44, the upper end of the weir duct 46 is disposed below the upper end 50a of the weir receptacle 44 by a distance d1, and the lower end of theweir duct is spaced laterally (or horizontally) apart from the interiorsurface 52 of the weir receptacle 44 by a distance d2 to define anannular opening 84 there between. The weir duct 46, the weir receptacle44, and the securement flange 78 may be formed from stainless steel orother metal. The securement flange 78 may be secured to the weir duct 46and the weir receptacle 44 by welding or in other suitable ways. Theweir 34 may be of other configurations without departing from the scopeof the claimed invention.

Referring to FIGS. 5 and 6, a weir trough 86 of the weir 34 is definedby the weir duct 46, the weir receptacle 44, and the securement flange78. In particular, the illustrated weir trough 86 is generally in theform of an annular channel, with the side wall 62 of the weir duct 46defining an inner side of the trough, the side wall 48 of the weirreceptacle 44 defining an outer side of the trough, and the securementflange 78 defining a bottom of the trough. The weir trough 86 at leastpartially surrounds the upper portion of the weir duct 46, and in theillustrated embodiment, the weir trough completely surrounds the upperportion of the duct. The weir trough 86 is configured to be at leastpartially filled with liquid during operation of the gas inlet system12. As shown in FIGS. 2 and 3, the illustrated weir trough 86 includesat least one trough inlet 90 (e.g., 4 inlets) extending through the weirreceptacle 44 (i.e., through the outer side of the trough 86). Theillustrated trough inlets 90 are configured to direct liquid in agenerally horizontal direction and tangentially along side wall 48 ofweir receptacle 44 so that the flowing liquid generally swirls aroundthe weir trough 86. The weir trough 86 and/or the inlet(s) 90 may beformed in other ways and may be of other configurations withoutdeparting from the scope of the claimed invention.

Referring to FIGS. 5-7, the weir trough 86 also has two trough outlets:an upper trough outlet 94 and a lower trough outlet defined by the atleast one opening 80 in the securement flange 78 (i.e., the bottom ofthe weir trough 86). The upper trough outlet 94 is at the upper end ofthe weir duct 46 and is in liquid communication with the upper weir ductinlet 68 to allow liquid in the weir trough 86 to overflow relative tothe weir duct such that liquid flows over the weir lip 72 at the upperend of the duct, through duct passage 66 and toward the weir outlet 56at the lower end of the weir 34. This overflow through the upper troughoutlet 94 is due to the upper end of the weir duct 46 being disposedbelow the upper end 50 a of the weir receptacle 44 (e.g., the outer sidewall of the trough is disposed above the inner side wall). Thus, in thisregard, the weir 34 functions as an overflow or leaping weir. The lowertrough outlet 80 is in liquid communication with a bypass 100 defined bythe lower portion of the weir duct 46 and the cone-shaped interiorsurface 52 of the lower portion of the weir receptacle 44. The bypass100 defines a bypass conduit 102 having a bypass outlet defined by theannular opening 84 between the lower end of the weir duct 46 and thecone-shaped interior surface 52 of the weir receptacle 44. Thecone-shaped interior surface 52 of the weir receptacle 44 funnels liquidtoward the bypass outlet 84. The bypass outlet 84 is in liquidcommunication with the weir outlet 56 and the scrubbing passage 37 toultimately fluidly connect the lower trough outlet 80 with the scrubbingpassage. Accordingly, the lower trough outlet 80 and the bypass 100function as a duct bypass to deliver liquid from the weir trough 86 tothe scrubbing passage 37 without flowing through the duct passage 66.Both the upper and lower trough outlets 94, 80, respectively (and thebypass outlet 84), are continuously open during operation of the gasinlet system 12, and the outlets are free from devices allowingselective flow obstruction. For example, the outlets 94, 80 are freefrom valves or other devices that allow for selective closure of theoutlets.

It is understood that one or both of the upper and lower trough outlets94, 80, respectively, may be formed in other ways in other embodiments.For example, the upper trough outlet may be formed as one or moreopenings in the side wall 62 of the weir duct 46. With respect to thelower trough outlet, in a non-limiting example, the outlet may be formedby a tube or conduit or other component. Moreover, in one non-limitingexample, the tube or conduit forming the lower trough outlet may beexternal or internal with respect to the weir receptacle. It is alsounderstood that the bypass 100 and the bypass outlet 84 may be formed inother ways. Moreover, the gas inlet system 12 may not include a separatebypass, such as the bypass 100. For example, the lower trough outlet 80may drain directly into the lower portion of the weir 34 and/or directlyinto the scrubbing passage 37, without directing liquid into the weirduct 46, whereby the lower trough outlet alone functions as a ductbypass. In another example, the lower trough outlet 80 may be in fluidcommunication with the duct passage 66, whereby a duct bypass is notpresent. Other configurations are possible within the scope of theclaimed invention.

A non-limiting embodiment of a method of using the illustrated gas inletsystem 12 will now be described. At the onset of operation, liquid isdelivered to the trough inlets 90 via the pump 22 or other device. Inthis example, liquid delivered to the weir trough 86 is scrubbing liquidfrom the same source that is in liquid communication with the jet nozzle32. From the trough inlets 90, the liquid flows into the weir trough 86in a generally horizontal direction and tangentially along side wall 48of weir receptacle 44, as described above, although the liquid may flowin any suitable direction. As the liquid initially enters the weirtrough 86, a portion of the liquid flows downward through the lowertrough outlet 80 (defined by the openings 80 in the securement flange78), through the bypass 100 and the weir outlet 56 as a liquid film andthen into the scrubbing passage 37 (thus bypassing the duct passage 66).The flow of liquid through the lower trough outlet 80 and through thebypass 100 is indicated by the arrows having reference characters F1 inFIG. 5. The flow rate of liquid into the weir trough 86 is greater thanthe net flow rate through the lower trough outlet 80, so that the weirtrough fills with liquid concurrently with liquid flowing through thelower trough outlet. When the weir trough 86 is filled with liquid abovethe weir lip 72 at the upper end of the weir duct 46, liquid overflowsthrough the upper duct inlet 68 and into the duct passage 66. The flowrate and distribution of the liquid over the weir lip 72 and into theduct passage 66 is such that the liquid flows as a thin film on theinterior surface 64 defining the duct passage. The thin film of liquidsubstantially covers the entire interior surface 64 of the weir duct 46and flows downward through the lower duct outlet 70. The flow of thethin film of liquid through the duct passage 66 is indicated by thearrows having reference characters F2 in FIG. 5. The liquid film F2exits the duct passage 66 and joins the liquid film F1 from the bypass100 at the lower, tapering portion of the weir receptacle 44 adjacentthe weir outlet 56 to form a combined thin film of liquid. The flow ofthe combined film of liquid is indicated by the arrows having referencecharacter F3 in FIG. 5. The combined film of liquid F3 flows downwardthrough the weir outlet 56 and then along the interior surface 36defining the scrubbing passage 37. The combined film of liquid F3substantially covers the entire interior surface 36 of the scrubbingvessel 30. Liquid continuously flows into the weir trough 86 via thetrough inlets 90, and liquid continuously and concurrently flows throughthe upper and lower trough outlets 94, 80, respectively, to produce acontinuous combined thin film of liquid F3 flowing downward along theinterior surface 36 defining the scrubbing passage 37.

Concurrently with the continuous combined liquid film F3 flowing alongthe interior surface 36 defining the scrubbing passage 37, scrubbingliquid is continuously delivered into the scrubbing passage via the jetnozzle 32 to produce an upward flow of scrubbing liquid in the scrubbingpassage. The upward flow of scrubbing liquid is indicated by the arrowshaving reference character F4 in FIG. 1. The scrubbing liquid may beintroduced via the jet nozzle 32 before, after, or concurrently with theinitial delivery of liquid into the weir trough 86. After forming thecontinuous combined film of liquid F3 and the upward flow of scrubbingliquid in the scrubbing passage 37, hot gas is introduced into thescrubbing passage via the gas inlet tube 38. Hot gas is continuouslydelivered into the scrubbing passage 37 concurrently with the continuousflow of the combined liquid film F3 and the upward flow of scrubbingliquid F4. The hot gas collides with the upward flow of scrubbing liquidF4 at the froth zone 40. In the froth zone 40, the gas/liquid interfaceis continuously and rapidly renewed. When the momentum of the gas andliquid balances, the liquid reverses direction and flows downward in thescrubbing vessel 30. The scrubbed gas and the spent liquid exit thescrubbing vessel 30 and enter the gas-liquid disengagement vessel 14.The continuous flowing liquid films F2 and F3 inhibit corrosion of therespective interior surfaces 36, 52 and 64 of the gas inlet system 12due to the hot gas flowing into the system.

The parameters of the gas inlet system 12, including but not necessarilylimited to the dimensions of the weir trough 86, the number and areas ofthe openings 80 of the securement flange 78, the area of the bypassoutlet 84 (i.e., the annular opening), and the flow rate of liquid intothe weir trough, are interdependent in order to achieve both the desiredwetting of the interior surfaces 36, 52 and 64 of the gas inlet system(i.e., the desired formation of the thin films F2, F3), and the desireddraining or flushing of the weir trough through the lower trough outlet80 to inhibit accumulation of particulates in the weir trough. Forexample, the individual area of each opening 80 in the securement flange78 should be large enough to inhibit particulates in the liquid fromclogging the outlet. However, if the area of each opening 80 is toolarge and/or if the number of openings is too numerous, the combinedflow rate through the openings may inhibit the weir trough 86 fromfilling with liquid, which would inhibit overflow of liquid through theupper trough outlet 94. Moreover, the flow rate into the weir trough 86and the volume of liquid held by the weir trough (and possibly otherparameters of the trough) also affects whether the weir troughappropriately fills with liquid such that the appropriate flow rate isachieved through the upper and lower trough outlets 94, 80,respectively, to produce the continuous flowing film F2, F3 along theinterior surfaces 36, 52 and 64 defining the scrubbing passage 37 andthe duct passage 66. If the flow rate of liquid through the upper andlower trough outlets 94, 80, respectively, is too high, the flowingliquid films F2, F3 may not be satisfactorily achieved because theliquid may detach from the interior surfaces. Moreover, if the flowrates through the upper and lower trough outlets 94, 80, respectively,is too low, the flowing liquid films F2, F3 may be too thin or may notadequately cover the interior surfaces 36, 52 and 64.

In one non-limiting example, parameters of the gas inlet system 12 maybe chosen by first establishing a flow rate of liquid into the weirtrough 86 and determining the height of the weir trough, whichdetermines the available pressure of the liquid in the trough. With theflow rate and pressure established, the combined or total open area ofthe openings 80 in the securement flange 78 (i.e., the openings inbottom of the trough) can be calculated to achieve a desired flow ratethrough the lower trough outlet, as defined by the openings. Then, thenumber of openings 80 (or drains) to install in the securement flange78, and the area of each, can be determined. More openings 80 isbeneficial in that the liquid would be introduced in more locations.However, each opening 80 would be smaller as the number of openingsincreased. If the openings 80 are too small, they could then becomeplugged. Thus, the location, the number and the size of the openingsshould be determined.

The gas inlet system 12, and more specifically the weir 34, may provideone or more of the following advantages during operation of the wet gasscrubber 10. As a non-limiting example, the weir 34 of the presentdisclosure inhibits build-up or accumulation of particulates in the weirtrough 86. During operation, the lower trough outlet 80 (e.g., theopenings 80 in the securement flange 78 defining the bottom of the weirtrough 86) continuously drains the weir trough to inhibit theaccumulation of particulates suspended in the liquid. Continuouslydraining the weir trough 86 has the effect of continuously flushing anyparticulates from the liquid that settle or could settle at the bottom78 of the weir trough. Moreover, the lower trough outlet 80 and thebypass 100 function as an internal drain system because the lower troughoutlet and bypass are contained within the gas inlet system 12 and drainliquid into the scrubbing passage 37 of the gas inlet system 12. Thus,external tubes or valves or pumps, which remove the particulates from aconventional gas inlet system, are not required to remove particulatesfrom the weir trough 86. As explained above, liquid flows through thebypass outlet 84 as a liquid film F1 on the interior surface 52 of theweir receptacle 44 and joins the liquid film F2 flowing out of the weirduct 46 to form a combined liquid film F3 that flows into the scrubbingpassage 37. In the illustrated embodiment, the two liquid films F1, F2join adjacent to and upstream from the weir outlet 56 to form thecombined liquid film F3. This combined liquid film F3 provides theadditional advantage of facilitating wetting of the interior surface 36defining the scrubbing passage 37. Moreover, if one of the liquid filmsF1, F2 fail, the other liquid film becomes a failsafe or backup thatcontinues to wet the scrubbing passage 37. Thus, the formation of oneliquid film (e.g., F1) is not dependent on the formation of the otherliquid film (e.g., F2) and vice versa (i.e., the liquid films formindependently of one another).

Example

The following is a non-limiting example demonstrating the process ofdetermining the parameters of the gas inlet system.

A goal of the design of the gas inlet system 12 is to have liquid flowrate of liquid the openings 80 in the securement flange 78 (i.e., liquidflow rate through the lower trough outlet) be equal to about 50% of theliquid flow rate over the upper end of the weir 34 (i.e., liquid flowrate through the upper trough outlet 94).

Using the above disclosed embodiment of the gas inlet system 12, beloware the steps and parameters used in the design of a working gas inletsystem.

The following parameters are first chosen or calculated:

-   -   Outer diameter of weir duct 46 is 48″, (or 4 feet).    -   Design criteria for flow over the weir duct 46 (i.e., flow rate        through the upper trough outlet) is 20 gpm per foot of the        perimeter of the weir duct.    -   F_(w)=Flow rate over the upper end of the weir duct (flow        through upper trough outlet)=π×4 feet×10 gpm/ft=252 gpm.    -   F_(h) =Flow through openings 80 in the securement flange 78        (flow rate through the lower trough outlet)=1/2×F_(w)=126 gpm    -   F_(t) =Total flow rate into the weir trough (combined flow rate        through trough inlets)=F_(w)+F_(h)=252 gpm+126 gpm=378 gpm

Next, the amount of open area required for the openings 80 in thesecurement flange 78 for a flow rate of 126 gpm is determined. Fromdesign above, there will be a liquid head, H, over the openings 80 inthe securement flange 78 of 10.5″. This assumes the weir trough 86 isfilled to the upper end of the weir. Since there will be flow over theweir duct 46, this is a reasonable assumption.

First, the velocity through each opening 80 is determined. The form ofthe equation is:H=K×(V ²/2 g)

-   -   H=liquid head in feet of water=10.5″/ 12″/ft=0.875 feet    -   K=resistance co-efficient=1 for a sudden enlargement.    -   V=velocity of the liquid through the opening 80 in feet per        second, which is the unknown to solve.

g=acceleration of gravity=32.2 ft/sec²

So, substituting the values:0.875 feet=1.0×(V ²/(2×32.2 ft/sec²)

Solving the above equation:

-   -   V=7.5 feet per second.

Next, the total area required for the openings 80 is solved, which willbe called A_(ht). The liquid flow is set at 126 gpm. Converting thisvalue to cubic feet per second, and then dividing by the velocity:F _(h)=126 gal/min×(ft³/7.48 gal)×(min/60 sec)=0.28075 ft³/sec.A _(ht) =F _(h) /V=0.28075 ft³/7.5 ft/sec=0.037433 ft²=5.3904 in²

The number of openings 80 to use is then selected. As the number ofopenings 80 increases, the area per opening will go decrease. Howeversmaller openings 80 are more prone to plugging. Moreover, too few ofopening 80 will lead to space between the openings increasing, and thiswill provide areas at the bottom 78 of the trough 86 for solids tobuild. The perimeter of the weir duct 46 is used a guideline since theflow rates are based off of it. The basis is to have 1 opening 80 at 6″intervals of the weir duct perimeter.

Weir duct perimeter=48″×π=150.8 inches. Therefore, number of openings is150.8″/6″ per opening=25.133 holes. Rounding this number off to theclosest whole number that is divisible by 4, the total number ofopenings is 24. Accordingly, the area required per opening=A_(ht)/# ofholes=5.3904 in²/ 24=0.2246 in² per opening.

The individual opening diameter, Dh, is determined from this area, asfollows:(π/4)×(D _(h) ²)=0.2246 in²

Then, Dh=0.535 inch.

Round this value off to the nearest fraction leads to:

-   -   Each of the 24 openings has a diameter of 17/32″.    -   Actual area per opening=(π/4)×(0.53125 in)²=0.22166 in²        A _(ht)=24×0.22166 in²=5.32 in²×(ft²/144 in²)=0.0369 ft²        F _(h)=(0.0369 ft²)×(7.5 ft/sec)×(60 sec/min)×(7.48 gal/ft³)=124        gpm.

The actual calculated flow through the openings 80 is 124 gpm, and isapproximately 49% of liquid flowing over the upper end of the weir duct46 and into the duct passage 66. Each opening has a 17/32″ diameterwhich should be sufficiently large to avoid plugging. Also, the openings80 are close enough to one another such that no large areas of thesecurement flange 78 are left unprotected from the build-up ofparticulate impurities.

The liquid that drains through the openings 80 must pass through theannular opening 84 (i.e., the bypass outlet) between the weir duct 46and the weir receptacle 44. The width of the annular opening 84 (definedby d2) is approximately ⅝″. Thus, the total area for the liquid to flowthrough the annular opening 84=(π×48 in×0.625 in)=94.25 in². This areais significantly greater than the combined area of the openings 80, andshould not cause a back-up or accumulation of liquid in the bypass 100.In addition, the liquid exiting the openings 80 will strike thecone-shaped interior surface 52 partially defining the bypass 100, whichwill tend to distribute this liquid around the entire perimeter of theinterior surface adjacent the annular opening 84.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

When introducing elements of the disclosed embodiments and the claimedinvention, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising”,“including” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

As various changes could be made in the above constructions, products,and methods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. A gas inlet system for a wet gas scrubbercomprising: a scrubbing vessel having an interior surface defining ascrubbing passage, the scrubbing vessel configured to receive a gas anda scrubbing liquid so that the gas contacts the scrubbing liquid duringoperation of the gas inlet system; a weir disposed above and in fluidcommunication with the scrubbing passage, the weir configured to deliverliquid to the scrubbing passage to wet the interior surface of thescrubbing vessel during operation of the gas inlet system, the weirincluding: a weir duct having at least one side wall, an interior weirduct passage, an upper weir duct inlet in fluid communication with theinterior weir duct passage, and a lower weir duct outlet in fluidcommunication with the weir duct passage, and a weir trough extending atleast partially around the at least one side wall of the weir duct andconfigured to receive and at least partially fill with liquid duringoperation of the gas inlet system, wherein the weir trough has an uppertrough outlet in liquid communication with the upper weir duct inlet andconfigured to deliver liquid from the weir trough into the upper weirduct inlet during operation of the gas inlet system, whereby liquid isdirected from the weir duct passage through the lower weir duct outletand toward the scrubbing passage to facilitate wetting of the interiorsurface of scrubbing vessel during operation of the gas inlet system,and wherein the weir trough has a lower trough outlet below the uppertrough outlet, the lower trough outlet in liquid communication with thescrubbing passage and configured to deliver liquid from the weir troughtoward the scrubbing passage during operation of the gas inlet system.2. The gas inlet system set forth in claim 1, wherein the weir troughincludes a bottom wall, the bottom wall having at least one openingdefining the lower trough outlet.
 3. The gas inlet system set forth inclaim 2, wherein the bottom wall has a generally annular shape andextends around a perimeter of the at least one side wall of the weirduct, the at least one opening of the bottom wall comprising a pluralityof openings spaced apart from one another around the bottom wall.
 4. Thegas inlet system set forth in claim 3, wherein the weir trough includesan outer trough side wall laterally spaced from and surrounding the weirduct, wherein the bottom wall comprises a securement flange extendinglaterally between and interconnecting the outer trough side wall and theweir duct.
 5. The gas inlet system set forth in claim 4, wherein theweir trough has a trough inlet disposed heightwise between the upper andlower trough outlets.
 6. The gas inlet system set forth in claim 1,wherein the lower trough outlet is configured to be free from liquidcommunication with the weir duct such that liquid flowing through thelower trough outlet does not pass through the weir duct during operationof the gas inlet system.
 7. The gas inlet system set forth in claim 6,further comprising a weir duct bypass intermediate and in liquidcommunication with the lower trough outlet and the scrubbing passage,wherein the lower trough outlet is configured to deliver liquid from theweir trough into the weir duct bypass without passing through the weirduct passage during operation of the gas inlet system, and wherein theweir duct bypass is configured to deliver liquid received from the lowertrough outlet toward the scrubbing passage without passing through theweir duct passage during operation of the gas inlet system.
 8. The gasinlet system set forth in claim 7, wherein the weir duct bypass has abypass outlet adjacent the lower weir duct outlet.
 9. The gas inletsystem set forth in claim 8, wherein the bypass outlet comprises acontinuous opening surrounding an entire outer perimeter of the sidewall of the weir duct.
 10. The gas inlet system set forth in claim 1,wherein the weir trough is configured such that liquid from the weirtrough concurrently flows through the upper and lower trough outletsduring operation of the gas inlet system.
 11. The gas inlet system setforth in claim 10, wherein the upper and lower trough outlets arecontinuously open and free from devices allowing selective flowrestriction.
 12. The gas inlet system set forth in claim 1, wherein theweir duct has an open upper end defining the upper weir duct inlet,wherein the weir trough includes an outer trough wall having an upperend disposed above the upper end of the weir duct, the upper troughoutlet defined between the upper ends of the weir duct and the weirtrough and allowing liquid in the weir trough to overflow relative tothe upper end of the weir duct and into the upper weir duct inlet duringoperation of the gas inlet system.
 13. The gas inlet system set forth inclaim 12, further comprising a jet nozzle disposed in the scrubbingpassage and configured to deliver scrubbing liquid into the scrubbingpassage during operation of the gas inlet system.
 14. The gas inletsystem set forth in claim 13, wherein the jet nozzle is configured todirect scrubbing liquid upward toward an upper portion of the scrubbingpassage during operation of the gas inlet system.
 15. The gas inletsystem set forth in claim 1, wherein the weir trough includes a bottomwall, the bottom wall having at least one opening defining the lowertrough outlet, wherein the weir duct has an open upper end defining theupper weir duct inlet, wherein the weir trough includes an outer troughwall having an upper end disposed above the upper end of the weir duct,the upper trough outlet defined between the upper ends of the weir ductand the weir trough and allowing liquid in the weir trough to overflowrelative to the upper end of the weir duct and into the upper weir ductinlet during operation of the gas inlet system, the gas inlet systemfurther comprising a weir duct bypass intermediate and in liquidcommunication with the lower trough outlet and the scrubbing passage,wherein the lower trough outlet is configured to deliver liquid from theweir trough into the weir duct bypass without passing through the weirduct passage during operation of the gas inlet system, and wherein theweir duct bypass is configured to deliver liquid received from the lowertrough outlet toward the scrubbing passage without passing through theweir duct passage during operation of the gas inlet system.